Swiss Patent Specification No. 411,536 discloses a centrifugal particle/gas separator in which the gas stream descends along a helical path in an annular separating zone and then rises inside the separating zone. That separator has a gas supply line which extends in the upper region from the inside into an annular separating zone and has at least one flow passage for the gas stream adjacent to the discharge zone.
The gas stream enters vertically from below and is then deflected outwardly initially in a horizontal radial direction, then in a tangential direction, then downwardly along a helical path, and then inwardly and finally upwardly. In addition, the gas stream appears to be divided into a plurality of partial streams so that the conditions for the separation are radially symmetrical.
The conducting of the gas along this extensive flow path involves a considerable drag and does not permit a satisfactory solids recovery factor to be achieved because the gas flows downwardly in a direction that is parallel to the movement of the subsiding solid particles so that particles which have already been separated may be re-entrained and discharged from the separator.